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// CAS-style: stale timer can't
// overwrite valid state transition
int _stateGeneration = 0;

void setError(String error) {
  _connectionState = VpnConnectionState.error;
  _stateGeneration++;
  final genAtError = _stateGeneration;

  // 5s recovery timer — but only if
  // no new state change happened
  _recoveryTimer = Timer(5.s, () {
    if (_stateGeneration == genAtError
        && _connectionState == .error) {
      _connectionState = .disconnected;
      _stateGeneration++;
    }
  });
}

// Serializes connect/disconnect ops
Completer<void>? _operationLock;

Future<bool> _acquireOperationLock()
    async {
  if (_operationLock != null
      && !_operationLock!.isCompleted) {
    try {
      await _operationLock!.future
        .timeout(30.s);
    } on TimeoutException {
      // Force-complete stale Completer
      // to unblock all waiters
      _operationLock!.complete();
    }
  }
  _operationLock = Completer<void>();
  return true;
}

// Macro: catch Rust panic at FFI
macro_rules! ffi_catch_unwind {
  ($body:expr) => {
    std::panic::catch_unwind(
      AssertUnwindSafe(|| $body))
      .unwrap_or(ERROR_RUNTIME)
  };
}

// CAS guards concurrent proxy ops
static UPDATING: AtomicBool = ..;

#[no_mangle]
pub extern "C" fn set_global(..) {
  ffi_catch_unwind!({
    // compare_exchange: AcqRel
    if UPDATING.compare_exchange(
      false, true,
      Ordering::AcqRel, Ordering::Acquire
    ).is_err() {
      return ERROR_BUSY;
    }
    let r = set_global_inner(..);
    UPDATING.store(false, Release);
    r
  })
}

// DynamicLibrary can't cross isolates
static List<int> _findInIsolate(
    _Params p) {
  final lib = p.libPath != null
    ? DynamicLibrary.open(p.libPath!)
    : DynamicLibrary.process();

  // Manual malloc/free lifecycle
  final name = p.name.toNativeUtf8();
  final pids = findByName(name.cast());
  malloc.free(name);
  // Length = -pids[0] (Rust convention)
  final len = -pids.value;
  freePidArray(pids); // Rust dealloc
}

// RAII: Finalizer = Rust Drop trait
static final _finalizer =
  Finalizer<void Function()>(
    (cb) => cb());
ProcessGuard._(handle) {
  _finalizer.attach(this,
    () => FFI.kill(handle),
    detach: this); // no double-free
}

// Store Future, not result — all
// concurrent callers share one flight
static final _inflight =
  <String, Future<Response>>{}

Future get(url) async {
  final key = 'GET:$url';
  if (_inflight[key] != null)
    return await _inflight[key]!;

  // Critical path → auto-race
  final f = isCritical(url)
    ? _raceGateways(url) : dio.get(url);
  _inflight[key] = f;
  try { return await f;
  } finally { _inflight.remove(key); }
}

// First-win: Completer + CancelToken
final c = Completer<Response>();
gateways.forEach((gw) => dio.get(
  gw + url, cancelToken: ct)
  .then((r) {
    if (!c.isCompleted) {
      c.complete(r); cancelOthers();
    }
  }));

// Triple pattern: dedup + grace + race
Future<String?> resolve(domain) {
  final cached = _cache[domain];
  if (cached != null) {
    if (!cached.expired) return cached.ip;
    // 60min grace: serve stale, refresh bg
    if (!cached.graceExpired) {
      _refreshInBackground(domain);
      return cached.ip;
    }
  }
  // Dedup: share Future for same domain
  return _pending.putIfAbsent(
    domain, () => _queryServers(domain));
}

// 3-level degradation + auto-recovery
enum Level { normal, degraded, emergency }
// emergency→degraded: 10min timer
// degraded→normal:    5min timer